A combustion engine, such as a diesel engine, a gasoline engine, and a gaseous fuel powered engine, is supplied with a mixture of air and fuel for combustion within combustions chambers of the engine to generate mechanical power output. The engine may include a turbocharger to help increase the power output generated by this combustion process. This typically includes a turbine driven by exhaust gases of the engine and a compressor driven by the turbine. The compressor receives a fluid, typically in the form of intake air, and supplies the compressed intake air to the combustions chambers. The turbocharger increases engine power by forcing more air into the combustion chambers than would otherwise be possible. This increased amount of intake air in the combustion chambers allows for higher combustion pressures that increase the power output generated by the engine.
In addition to increasing engine power output and efficiency, it is desirable to simultaneously minimize exhaust emissions. Combustion engines exhaust a complex mixture of air pollutants as byproducts of the combustion process, and due to increased attention to the environment, exhaust emissions standards have become more stringent. The amount of pollutants emitted to the atmosphere from an engine can be regulated depending on the type of engine, size of engine, and/or class of engine.
One method that has been implemented to help comply with the regulation of these exhaust emissions includes utilizing an exhaust gas recirculation (EGR) system. EGR systems operate by recirculating a portion of the exhaust produced by the engine back to the intake of the engine to mix with fresh air. The resulting mixture has a lower combustion temperature and, subsequently, produces a reduced amount of regulated pollutants.
U.S. Pat. No. 6,694,736 B2 issued to Plfüger on Feb. 24, 2004 (the '736 patent) discloses a turbocharged internal combustion engine with a plurality of exhaust turbines, including a high-pressure stage turbocharger set, a low-pressure stage turbocharger arranged downstream of the high-pressure stage turbocharger set, and an exhaust return flow for feeding exhaust to the intake air of the engine. The high-pressure stage turbocharger set includes two high-pressure turbines arranged in parallel, and the low-pressure stage turbocharger is arranged in series with the two high-pressure stage turbines. The multi-stage turbine system provides high boost pressure, and thus, increased power output of the engine.
Although the engine system of the '736 patent may provide high boost for higher engine power applications, it may have limitations. For example, the single low-pressure turbine of the low-pressure stage may have poor efficiency at high boost production levels.
The engine system of the present disclosure is directed towards improvements to existing technology.